[Radiance-general] daylight factor and rtrace cmd

[Thomas Bleicher]

Hi Greg. Still awake or are you traveling again?

On Fri, Jul 17, 2009 at 7:02 AM, Greg Ward<gward at lmi.net> wrote:

> I'm not sure what you mean, though, about the -I option changing the effect
> of -ab.  I suppose it depends on how you think about it.  With -ab set to 0,
> only direct illumination arriving at that position is considered.  Setting
> -ab 1 sends out sample rays over the hemisphere to gather indirect
> contributions.  Is this other than what you would expect?

Perhaps it's me being extremely blond about the meaning of "-i" vs "-I".

Consider a scene with a sky and a plane just below z=0.
I am now looking down from z=1 onto the plane and get:

$ echo "0 0 1 0 0 -1" | rtrace -h -i -ab 0 scene.oct
2.541776e+01    2.541776e+01    2.541776e+01

$ echo "0 0 1 0 0 -1" | rtrace -h -i -ab 1 scene.oct
7.457800e+01    7.457800e+01    7.457800e+01

$ echo "0 0 1 0 0 -1" | rtrace -h -I -ab 0 scene.oct
0.000000e+00    0.000000e+00    0.000000e+00

$ echo "0 0 1 0 0 -1" | rtrace -h -I -ab 1 scene.oct
2.033156e+01    2.033156e+01    2.033156e+01

Why do I get different values for "-i" for "-ab 0" and "-ab 1"?
There is nothing in the scene to bounce light off.

And why do I get "0 0 0" for "-ab 0" when i use "-I" but not
when I use "-i". For "-ab 0" I would have expected both of them
to be zero.


Thomas